The present invention relates generally to apparatus for plasma treatment, and more particularly to a plasma treatment system that offers an improved automated processing capability.
Gas plasma treatment of a variety of substrates, particularly those in the electronics field, is a well-established and proven process that increases surface activation (wettability), improves die attach, increases the reliability and strength of wire bonds, and provides better adhesion for encapsulation. Plasma systems have been in use for over 25 years for such applications and offer significant advantages over liquid chemical treatment methods and other dry methods such as ozone.
Disclosed in U.S. Pat. No. 4,208,159, issued to Uehara et al. on 17 Jun. 1980, is an apparatus that performs, in an automated assembly line manner, the plasma treatment of individual electronic parts, namely, semiconductor wafers. Prior to the invention of Uehara, plasma treatment of electronic parts was performed in batch-wise fashion. As Uehara describes, such simultaneous plasma treatment of a large number of parts generally does not result in an even reaction (i.e., etching or cleaning) at the surface of a substrate. Batch-wise treatment also reduces productivity by interrupting the flow of processing and assembly of parts.
Uehara provides for a reaction chamber having an open bottom portion and a wafer xe2x80x9ctablexe2x80x9d that moves vertically up and down to be vacuum-sealable with the opening of the reaction chamber. The apparatus further includes an in-take carrier means for carrying a wafer to a position adjacent the wafer table, and an in-take pick-up means for picking up the wafer from the in-take carrier means and placing the wafer onto the wafer table. Disclosed in the patent are two combinations of such in-take carrier and pick-up means, one of which employs two revolving arms, each having a suction type pick-up, the other of which employs two linear traveling arms, each having a suction pick-up as well. After the single wafer has been placed on the wafer table, the wafer table is raised to seal against the reaction chamber and the plasma process is initiated. Out-take means identical to the in-take carrier and pick-up means are used for removal of the treated wafer from the wafer table after the wafer table has been disengaged and lowered from the reaction chamber opening.
The invention of Uehara offers substantial advantages in that it makes possible the in-line, hands-off plasma processing of individual parts (wafers). However, both of the embodiments disclosed are much more limiting in their scope of operation than is desirable. The invention does not allow, when it is desired, for the plasma treatment of more than one part at a time. It was noted previously that individual processing of parts is advantageous with respect to the evenness of the plasma reaction that may be obtained. However, it is also the case that a sufficiently uniform reaction may be obtained, depending on the nature of the parts (and upon appropriate spacing therebetween), where more than one part at a time is treated. Uehara does not address this issue. In addition, pick-up mechanisms of the type shown in Uehara, which as noted is in the form of a suction device, are known to be not entirely free from droppage and breakage of parts due to temporary loss or irregularity of vacuum pressure.
Shown in U.S. Pat. No. 4,318,767, issued to Hijikata et al. on 9 Mar. 1982, is another automatic in-line plasma system for treatment of semiconductor wafers. Hijikata employs a non-movable reaction chamber with a vertically movable wafer table contained therein. Shutter-like slits, which are vacuum-sealable and which are present at opposing ends of the reaction chamber, provide entry and exit portals for the wafers. The wafers are introduced into the reaction chamber with a pair of slidable parallel arms spaceably distanced so as to support a wafer therebetween. In the process sequence, a single wafer is loaded onto the ends of the arms via a conveyor belt apparatus. The arms then slide forward to extend into the reaction chamber through the entry portal such that the wafer is positioned over the wafer table. The wafer table moves upward to a height just above the arms, lifting the wafer off of the arms in the process. After the arms have been retracted, the entry slit is sealed, the chamber evacuated, and the plasma process initiated to treat the wafer lying on the table. The wafer is removed by extension through the exit portal of a pair of arms identical to the ones previously employed followed by a lowering of the wafer table, which causes the treated wafer to rest upon the arms. Retraction of the arms then removes the wafer from the chamber.
Hijikata eliminates the precarious suction pick-up arrangement of Uehara, but again fails to offer an option for treating more than one part at a time in an in-line fashion. Nor is the invention of Hijikata amenable to such, since even were more than one part crudely loaded onto the ends of the sliding arms of the apparatus, no mechanism is available for properly spacing the parts upon the wafer table, such spacing being critical when more than one part is subjected to plasma treatment.
U.S. Pat. No. 4,889,609 to Cannella discloses an automated dry etching system which is titled xe2x80x9cContinuousxe2x80x9d but utilizes input and output belts which are enclosed in pressurized chambers which are maintained at a preselected partial vacuum. The enclosed nature of these chambers necessarily limits the number of parts that can be treated before the chambers have to be opened for loading a new batch to be processed. Additionally, the configuration of the input gate allows a very limited number of parts to be treated at once, and consequentially, the throughput of this system can be expected to be likewise limited.
U.S. Pat. No. 4,252,595 to Yamamoto et al. illustrates a plasma etching apparatus which includes a rotatable disk in the etching chamber, or alternately, a conveyer assembly, which is also included within the plasma chamber. Both of these variations can be expected to have problems related to the use of moving parts within the plasma chamber. Moving parts typically require lubricants, which can, over time, contaminate the etching chamber and the treated parts. Especially in near vacuum conditions, out-gasing of lubricants can be expected, and effects of even minute amounts of contaminants can be cumulative over time. Additionally, when moving parts are exposed to conditions such as in a plasma etching chamber, these parts are susceptible to corrosion. Moving parts which operate on fine tolerances can be expected to require frequent replacement when exposed to such harsh operating conditions.
U.S. Pat. No. 5,587,205 to Saito et al. also shows a plasma processing method including an electrode stage on a lifting mechanism. These moving parts can be expected to experience the same difficulties of contamination and corrosion discussed above. Additionally, the throughput of the system would appear to be very limited.
U.S. Pat. No. 4,405,435 to Tateishi et al. discloses a plasma treatment apparatus, but there is an elevator in the etching chamber, thus introducing moving parts. Once again, these moving parts can be expected to experience the same difficulties of contamination and corrosion discussed above.
Because of the limitations associated with most presently available plasma treatment systems, a substantial need still exists for such a system as offers improved processing capability while also providing for the simultaneous treatment of a plurality of parts.
Accordingly, it is an object of the present invention to provide a plasma treatment system that provides an automated, processing capability of electronic and other parts.
It is another object of the invention to provide a plasma treatment system capable of treating a plurality of parts at once.
It is a further object to provide a plasma treatment system that provides precise spacing for the treatment of a plurality of parts.
It is yet another object to provide a plasma treatment system that utilizes guide rails together with a distinct push mechanism for conveyance of the parts to be treated.
It is yet a further object to provide a plasma treatment system that employs infrared sensing devices to aid in the detection and positioning of the parts to be treated.
It is still another object to provide a plasma treatment system wherein no moving parts of the system are present within the reaction chamber during the treatment process.
It is a still further object to provide a plasma treatment system whereby parts may be treated on multiple levels within the reaction chamber.
It is yet another object of the present invention to provide a DC bias to the electrodes in order to promote better penetration of plasma between parts.
It is still another object of the present invention to increase ionization rates, and increase the energy of the ions and electrons to thus increase etch rates and decrease processing time.
It is a still further object of the present invention to provide more directional etching, resulting in more anisotropic etching, by using a DC bias.
It is an additional object of the present invention to provide a plasma treatment system which utilizes vertically oriented electrodes to provide better uniformity of treatment of parts.
Briefly, the preferred embodiment of the present invention is a plasma treatment system having an automated processing ability. The preferred embodiment is directed toward plasma treatment of PC boards but is generally applicable to any substrate susceptible of plasma reaction. For the purposes of discussion, the typical object substrate is referred to as a PC board, although it is recognized that it could well be a wafer or other object. The plasma treatment system has the primary components of a reaction chamber and chamber base, a chamber lifting assembly, a conveyor input assembly, a push mechanism and associated linear drive assembly, an output assembly, an electronic control system, and vacuum and plasma generating systems.
The conveyor input assembly includes a conveyor which rides upon a conveyor position actuator. A PC board is loaded onto the conveyor from, for example, a preceding belt-type conveyor in an overall assembly line process. The reaction chamber is lifted vertically via the chamber lifting assembly, and the conveyor is moved by the conveyor position actuator to be in aligned juxtaposition with the load end of a pair of chamber guide rails which are present within the perimeter of the chamber base and which are further supported atop a reaction-inducing electrode. The push mechanism moves the PC board from the conveyor and onto the chamber guide rails. The conveyor is then moved back to the starting position so that another PC board may be conveyed and carried by the conveyor. The second PC board is also transferred onto the chamber guide rails by the push mechanism.
The push mechanism employs first and second catch actuators that lower and raise first and second catch fingers. The first and second catch fingers extend into the travel area of the PC boards and, in the lowered position, are able to abuttably engage the PC boards and move them to any desired location along the conveyor or chamber guide rails. The catch fingers are raised when it is desired that the push mechanism pass unhindered above the travel area of the PC boards. First and second catch sensors located on the push mechanism, together with similar sensors located on the linear drive assembly, provide infrared detection so that the push mechanism may locate the PC boards and also properly space the PC boards upon the chamber guide rails for a uniform plasma reaction.
After multiple PC boards have been loaded onto the chamber guide rails, the reaction chamber is lowered upon the chamber base, whereon it is vacuum-tightly fittable, and plasma treatment is initiated using conventional plasma generating elements. When treatment is complete, the reaction chamber is raised, and an output carrier is moved into juxtaposition with an unload end of the chamber guide rails and the push mechanism is caused to unload the PC boards in an analogous fashion to the loading process.
A DC bias circuit can be included in the plasma treatment system to increase the directionality of plasma flow and the energy level of the ions and electrons in the plasma. The higher energy level also increases the ionization rate, thus increasing the number of ions and electrons. The increased energy level and increased ionization rate both act to produce a higher etching rate and thus a shorter processing time. The increased bias also results in a more directional flow of ions onto the parts, resulting in a more anisotropic etching which is required when etching vias and holes.
An alternative embodiment incorporates a multi-level arrangement to provide that two or more levels of PC boards may be simultaneously treated by plasma reaction. In the alternative embodiment, the PC boards are moved by a push mechanism similar to that employed in the single level embodiment, but having additional catch fingers capable of being positioned at heights as correspond to the distance between an upper and lower pair of chamber guide rails arranged in bi-level array upon the chamber base. A first PC board is initially transferred by the push mechanism from a stationary conveyor and onto the upper level of an input carrier also having a bi-level array of input guide rails spaceably distanced identically to the chamber guide rails. A first vertical position actuator raises the input carrier to bring the lower level of the input carrier into alignment with the level of the stationary conveyor so that a second PC board may then be moved onto the input carrier by the push mechanism.
The input carrier, carrying the two PC boards, is moved by a first horizontal position actuator to be near the chamber guide rails. The push mechanism then simultaneously transfers both PC boards onto the upper and lower chamber guide rails. The input carrier then moves back to be adjacent to the stationary conveyor and two additional PC boards are reloaded as before. The additional PC boards are also transferred onto the chamber guide rails by the push mechanism, and the reaction chamber is lowered and the plasma process is begun as for the single-level embodiment. An output carrier identical to the input carrier is employed to remove the PC boards after treatment is complete. As in the first embodiment, a DC bias circuit can be included in the plasma treatment system to increase the directionality of plasma flow. When this DC bias is applied to vertical electrodes, a horizontal flow is established that improves penetration in the clearance spaces between parts which have been placed in multilevel arrays. This improved penetration allows closer spacing of layers, while still maintaining good uniformity of treatment. Thus, throughput of parts can be increased.
A third preferred embodiment is a plasma treatment system for treating parts, which includes a reaction chamber, a device for supporting a number of parts in a multilevel array and a mechanism for generating a gas plasma and inducing a plasma reaction with the parts. The gas plasma mechanism includes devices for applying Radio Frequency (RF) power and DC bias power to the gas plasma. This is done by providing one or more electrodes through which RF is used to excite the gas to a plasma state, and the DC bias is also applied to one or more electrodes. This DC bias is used to direct the flow of the plasma, increase the Ionic energy, and increase the Ionization rate. By using vertically oriented electrodes, the plasma can be made to flow horizontally between the layers of a multilevel array that holds parts that are to be treated. The applied DC bias causes a more defined directionality of flow, which allows better penetration of the plasma to the multilevel array, and creates more uniformity of treatment. This improved penetration also allows closer spacing of parts and levels in a carrier, so that a carrier may have numerous levels configured into a xe2x80x9ccassettexe2x80x9d or xe2x80x9cmagazinexe2x80x9d. Use of a magazine which carries a large number of parts allows increased throughput of parts, in either in-line, batch-processing or systems which use robotics.
An advantage of the present invention is that a plurality of parts may be subjected to plasma treatment simultaneously in an in-line fashion, thereby speeding up processing time.
Another advantage of the invention is that none of the moving parts of the system are subjected to degradation from plasma reaction.
A further advantage is that the system is entirely automated, thereby providing hands-free operation.
Yet another advantage of the invention is that parts may be loaded within the reaction chamber on multiple levels, thereby multiplicatively increasing the throughput of parts.
An additional advantage of the invention is that vertically oriented electrodes permit better flow of the plasma over parts which are horizontally placed, and thus more uniformity of treatment of the parts is achieved.
Another advantage of the present invention is that by using an increased DC bias, there is better penetration of the plasma between parts in multilevel arrays.
Yet another advantage of the present invention is that improved penetration allows closer spacing of levels of parts in a multilevel array, thus allowing more levels to be placed in a given vertical space.
A still further advantage of the present invention is that by using an increased DC bias, higher energy ions and electrons are produced, and ionization rates are increased, both of which act to increase etching or cleaning rates.
A yet further advantage of the present invention is that throughput capabilities of the treatment system is increased, and processing time is reduced for systems which use in-line processing, for those which use batch-processing and for those which use robotics to handle materials.
These and other objects and advantages of the present invention will become clear to those skilled in the art in view of the description of the best presently known mode of carrying out the invention as described herein and as illustrated in the several figures of the drawings.